1. Field of the Invention
The invention relates to an electromechanical brake booster.
2. Description of the Prior Art
One such electromechanical brake booster is known from German Published Patent Application DE 103 27 553 A1. The known brake booster has a piston rod, which mechanically connects a brake pedal to a piston of a master cylinder. The term “piston rod” as used in terms of the invention should be understood in general to mean a connecting element which connects a brake pedal mechanically to a piston of a master cylinder, regardless of the shape of the connecting element, or in other words even if the shape of the connecting element is not reminiscent of a rod. Instead of a brake pedal, some other user control element for actuating a vehicle brake system by muscle power may be provided, such as a hand brake lever. The term “brake pedal” should be understood generally to mean a user control element of this kind. The piston rod of the known brake booster has a slaving means, which cooperates with a spindle of a helical gear. The spindle is a hollow spindle, and it concentrically surrounds the piston rod. A nut of the spindle drive is at the same time a rotor of an electric motor of the electromechanical brake booster. The electric motor having the spindle drive may be conceived of as an electromechanical auxiliary force generator, which when current is supplied exerts an auxiliary force via the slaving means on the piston rod, which increases an actuation force exerted by muscle power. If the brake pedal is stepped on hard in the event of rapid actuation of the brake, for instance in an emergency braking situation, the piston rod can lead ahead of the threaded spindle, and then the vehicle brake system is actuated exclusively by muscle power. A vehicle driver need not also accelerate the spindle and the spindle nut that is simultaneously the rotor of the electric motor.